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Page 3 — - West Lauffer Road Property February 16,2006 = Job No. 2836-001 - REGIONAL SETTING _ /PHYSICAL SETTING SOURCES Sources used to determine the regional setting during this study have included the following: • 1977 CGS Geologic Map of California (1:750,000) • 1994 CGS Fault Activity Map of California(1:750,000) - _- • 1981 CGS Geologic Map of the Sacramento Quadrangle (1:250,000) • 1985 USGS Geologic Map of Late Cenozoic Deposits of the Sacramento Valley(1:62,500)knFaf • 1978 USGS Thornton Quadrangle(1:24,000) • Appended EDR Radius Map database listing(including various area maps) _ GEOLOGICALIHYDROGEOLOGICAL CHARACTERISTICS /Geology ; The subject property is situated in the Sacramento Valley, and within the central portion of the Great Valley geomorphic province of California. The Geologic Map of California, Sacramento Sheet, indicates that sands, silts, clays, and peat in this portion of the Delta area are recognized as intertidal deposits (peaty mud). Nearly one-half of the total river volume of California flows through the Delta. The Delta is uncommon in that it grows landward rather than seaward as sediments derived largely from the Sierra Nevada area are deposited around its margins during higher sea levels, as at present. Conversely, the Delta contracts during geologic times of lower sea levels. Peat lands in the Delta have been subject to considerable subsidence since they were cleared for agricultural use. The loss of peat is generally due to oxidation, wind, and desiccation. /The near surface intertidal deposits are underlain by other Cenozoic continental and marine sediments and the upper Cretaceous geologic formation of the Great Valley Sequence. The formations within-- '' the sequence are several thousand feet thick. The Great Valley sediments are in turn, underlain by the- Mesozoic metamorphic and plutonic rocks of the Sierra Nevada. Hydrogeology Surface Water/Flood Potential The subject property is situated at an approximate elevation equal to mean sea level. The center line of the Mokelumne River Levee defines the westerly border of the subject property; most of the property"s site relief (about ten feet) is located along this levee., The Mokelumne River is situated along the westerly margin of the site. In the site vicinity, this river generally flows in a south-southwesterly direction. At the time of our reconnaissance, the.river appeared to be at a relatively high stage due to winter rains. Topography in the immediate vicinity trends gently to the west; surface water generated on the property would generally infiltrate site surface soils. When infiltration rates are exceeded, surface water would a1212ear to flow into a series of irrigation/dLainage ditcbetjjajCdqt pZQpegyJb9 qd_4 gs. No suspicious runoff to or from the site was observed during our recent site visit. _ The appended EDR report indicates that the general vicinity is located w' - e; our Iry study has not included a site specific flood zone determination. —�